Fully Biobased Adhesive from Chitosan and Tannic Acid with High Water Resistance

In this study, we developed a fully biobased adhesive using chitosan and tannic acid, drawing inspiration from natural mussel adhesive mechanisms. Our goal was to address the technological challenges associated with creating environmentally friendly adhesives that can perform comparably to their synthetic counterparts, particularly in terms of water resistance. The methodology involved the molecular complexation of chitosan, a polysaccharide rich in amine groups, with tannic acid, which is known for its galloyl moieties. This complexation mimics the dopa-lysine synergy found in mussel adhesives, leading to a cohesive and adhesive material under the right pH conditions. Notably, after mild thermal curing (70 °C for 2 h), our biobased adhesive demonstrated outstanding water resistance and long-term durability. It maintained a lap shear strength of approximately 3.5 MPa even after immersion in water for 2 months and could be stretched and released more than 1000 times before breaking. These performance metrics surpassed those of a commercial water-resistant adhesive, Gorilla Glue, and a well-known strong dry adhesive, Loctite Super Glue (both cured under their recommended conditions). The success of this adhesive underscores the importance of leveraging nature's mechanisms, such as molecular complexation and bioinspired chemistry, in developing next-generation biobased adhesives that overcome the challenge of poor water resistance. This biobased adhesive has potential applications as a sustainable alternative to petroleum-based adhesives, while the price and availability of the biobased raw materials need continuous evaluation.